U.S. patent number 6,287,506 [Application Number 09/112,532] was granted by the patent office on 2001-09-11 for method for reducing dilation balloon cone stiffness.
This patent grant is currently assigned to Schneider (USA) Inc.. Invention is credited to Robert C. Farnan, R. Garryl Hudgins.
United States Patent |
6,287,506 |
Hudgins , et al. |
September 11, 2001 |
Method for reducing dilation balloon cone stiffness
Abstract
A method for stretch blow molding dilatation balloons for
angioplasty catheters having a significantly reduced cone thickness
without sacrifice in burst strength is achieved by utilizing a mold
whose cavity includes arcuate walls defining the balloon's end
cones and a predetermined minimal distance from the side edges of
the mold to the points where the arcuate walls intersect with a
smaller diameter balloon stem portion. Utilizing this mold and
providing for three longitudinal stretching sequences, one prior
to, one during and one following radial expansion of the heated
plastic parison, results in an improved balloon exhibiting reduced
cone stiffness.
Inventors: |
Hudgins; R. Garryl (Lino Lakes,
MN), Farnan; Robert C. (Flagstaff, AZ) |
Assignee: |
Schneider (USA) Inc.
(Minneapolis, MN)
|
Family
ID: |
22344403 |
Appl.
No.: |
09/112,532 |
Filed: |
July 9, 1998 |
Current U.S.
Class: |
264/515; 264/532;
264/573; 264/900; 604/96.01; 606/194 |
Current CPC
Class: |
A61M
25/1029 (20130101); B29C 49/00 (20130101); A61M
2025/1084 (20130101); B29C 2049/0089 (20130101); B29K
2105/258 (20130101); B29L 2031/7542 (20130101); Y10S
264/90 (20130101) |
Current International
Class: |
A61M
25/00 (20060101); B29C 49/00 (20060101); B29C
049/04 (); B29C 049/08 () |
Field of
Search: |
;264/532,573,515,521,900
;604/96 ;606/194 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
88300025.9 |
|
May 1988 |
|
EP |
|
274 411 |
|
Jul 1988 |
|
EP |
|
89118420.2 |
|
Oct 1989 |
|
EP |
|
0 485 903 |
|
May 1992 |
|
EP |
|
0513 459 A1 |
|
Nov 1992 |
|
EP |
|
420 488 B |
|
Jul 1993 |
|
EP |
|
0 566 755 A1 |
|
Oct 1993 |
|
EP |
|
566 755 |
|
Oct 1993 |
|
EP |
|
540 858 |
|
Dec 1993 |
|
EP |
|
0 592 885 |
|
Apr 1994 |
|
EP |
|
0 730 879 |
|
Sep 1996 |
|
EP |
|
2 651 681 |
|
Mar 1991 |
|
FR |
|
84/01513 |
|
Apr 1984 |
|
WO |
|
92/8512 |
|
May 1992 |
|
WO |
|
92/19316 |
|
Nov 1992 |
|
WO |
|
WO 95/23619 |
|
Sep 1995 |
|
WO |
|
95/23619 |
|
Sep 1995 |
|
WO |
|
96/04951 |
|
Feb 1996 |
|
WO |
|
WO 96/12516 |
|
May 1996 |
|
WO |
|
WO 97/03716 |
|
Feb 1997 |
|
WO |
|
Other References
Flesher, "Polyether block, amide, high-performance TPE, "Modern
Plastics, Sep. 1987, pp. 100, 105, 110. .
Koch, "PEBAX (Polyether Block Amide)", Advances in Polymer
Technology, vol. 2, No. 3 1982 pp. 160-162. .
De, et al. eds. Thermoplastic Elastomer From Rubber-Plastic Blends,
Chapter 1, Ellis Horwoal, New York pp. 13-27. .
Gorski, "The Nomenclature of Thermoplastic Elastomers, "Kunstoffe
German Plastics, 83 (1993) No. 3, pp. 29-30. .
Hofman, "Thermoplastic Elastomers, "Kunstoffe German Plastics, 80
(1990) No. 10, pp. 88-90. .
Atochem, "Pebax Resins 33 Series Property Comparison" undated, (1
pg. manufacturers technical information sheet received Sep. 29,
1994). .
Atochem, undated and untitled brochure for Pebax resisn, pp. 2-5.
.
Bhowmick, et al eds. Handbook of Elastomers, Chapter 10 and 12,
Marcel Dekker Inc., pp. 341-373 and 411-442. .
Walker, et al, eds. Handbook of Thermoplastic Elastomers, Chapter
8, Van Nostrand Reinhold Co., NY pp. 258-281..
|
Primary Examiner: Silbaugh; Jan H.
Assistant Examiner: McDowell; Suzanne E
Attorney, Agent or Firm: Vidas, Arrett & Steinkruas
P.A.
Claims
What is claimed is:
1. A method of making dilatation balloons with reduced cone
stiffness, comprising the steps of:
(a) providing a mold having a cavity therein including a center
section of a predetermined diameter defining a working length for a
balloon to be formed therein and opposed end cone segments, each
defined by an arcuate wall tangent to a wall defining the generally
cylindrical center section and terminating in a cylindrical end
segment corresponding to a desired shaft size for the balloon to be
formed therein, the mold having opposed side edges spaced less than
0.25 inch from a point of intersection of the arcuate wall and the
cylindrical end segment;
(b) placing a tubular parison of a predetermined polymeric
composition across the mold cavity, the tubular parison having
opposed ends extending outwardly from the opposed side edges of the
mold;
(c) clamping the opposed ends of the tubular parison in
longitudinally displaceable tensioning fixtures;
(d) heating the mold to a temperature above the glass transition
temperature of the polymeric composition of the parison;
(e) longitudinally displacing the tensioning fixtures relative to
the mold a first time to effect a first predetermined stretch
ratio;
(f) subsequently longitudinally displacing the tensioning fixture
relative to the mold a second time to effect a second predetermined
stretch ratio while simultaneously injecting a gas, under pressure,
into the tubular parison to radially expand the parison against the
walls defining the mold cavity and thereby form a balloon having a
generally cylindrical center segment, a pair of opposed cone
segments and a pair of opposed shaft segments;
(g) further longitudinally displacing the tensioning fixture
relative to the mold a third time to effect a third stretch ratio,
the spacing of the opposed ends of the mold and the arcuate wall
configuration of the mold end cone segments configured to effect
selective thinning of the balloon cone and shaft segments;
(h) heating the mold to the crystallizing temperature of the
polymeric composition;
(i) cooling the mold to a temperature below the glass transition
temperature of the polymeric composition; and
(j) removing the resulting balloon from the mold.
2. The method as in claim 1 and further including a step of
pretensioning the tubular parison prior to step (d).
3. The method as in claim 1 wherein the polymeric composition
comprises PET.
4. The method as in claim 3 wherein the first predetermined stretch
ratio is in a range of from 1.005 to 2.0.
5. The method as in claim 3 wherein the second predetermined
stretch ratio is in a range of from 1.05 to 3.0.
6. The method as in claim 3 wherein the third stretch ratio is in a
range of from 1.1 to 4.0.
7. The method as in claim 1 wherein the tubular parison is a
co-extrusion of Nylon 12 over PET.
8. The method as in claim 1 wherein the gas injected is at a
pressure in a range of from 50 psi to 400 psi.
9. A method of fabricating a dilatation balloon in a stretch blow
molding operation comprising the steps of:
(a) providing a mold having a cavity formed therein defining a
desired shape configuration of a dilatation balloon to be formed
therein, the mold including a cylindrical central section and
opposed generally conical end sections tapering to a reduced
diameter shaft segment, each shaft segment extending axially to a
side edge, wherein the generally conical end sections comprise
arcuate boundaries defining the opposed generally conical end
sections;
(b) placing a tubular parison of a polymeric composition having a
predetermined diameter and wall thickness across the mold with
opposed ends of the parison extending outward beyond the side edges
of the mold;
(c) clamping the opposed ends of the parison in a tensioning
fixture;
(d) heating the mold to a temperature above the glass transition
temperature of the polymeric composition;
(e) simultaneously inflating and longitudinally displacing the
tensioning fixture relative to the mold to thereby stretch the
parison to form a balloon within the mold cavity and thereby form a
balloon having a generally cylindrical center segment, a pair of
opposed generally conical end segments and a pair of opposed shaft
segments;
(f) subjecting the balloon of step (e) to a further longitudinal
stretch within the heated mold to draw polymeric material from the
generally conical end sections without appreciable thinning of the
central section thereof, the spacing of the opposed ends of the
mold and the arcuate boundary configuration of the general conical
end segments configured to effect selective thinning of the balloon
cone and shaft segments relative to the central portion;
(g) heating the mold to a crystallizing temperature of the
polymeric composition;
(h) cooling the mold back down below the glass transition
temperature of the polymeric composition; and
(i) removing the balloon from the mold.
10. The method as in claim 9 wherein the arcuate boundaries are
tangent at one end to a segment defining the central section of the
balloon and intersect the segment defining the balloon shaft at
another end.
Description
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to dilatation balloon catheters of
the type employed in percutaneous transluminal angioplasty
procedures, and more particularly to a method of molding such
balloons to reduce their cone stiffness and thereby improve the
maneuverability in smaller and more tortious passages of the
vascular system.
II. Discussion of the Prior Art
Dilatation balloon catheters are well known for their utility in
treating the build-up of plaque and other occlusions in blood
vessels. Typically, a catheter is used to carry a dilatation
balloon to a treatment site, where fluid under pressure is supplied
to the balloon, to expand the balloon against a stenotic
lesion.
The dilatation balloon is affixed to an elongated flexible tubular
catheter proximate its distal end region. When the balloon is
expanded, its working length, i.e., its medial section, exhibits a
diameter substantially larger than that of the catheter body on
which it is mounted. The proximal and distal shafts or stems of the
balloon have diameters substantially equal to the diameter of the
catheter body. Proximal and distal tapered sections, referred to
herein as "cones", join the medial section to the proximal and
distal shafts, respectively. Each cone diverges in the direction
toward the medial section. Fusion bonds between the proximal and
distal balloon shafts and the catheter form a fluid-tight seal to
facilitate dilation of the balloon when a fluid under pressure is
introduced into it, via an inflation port formed through the wall
of the catheter and in fluid communication with the inflation lumen
of the catheter.
Along with body tissue compatibility, primary attributes considered
in the design and fabrication of dilation balloons are their
strength and pliability. A higher hoop strength or burst pressure
reduces the risk of accidental rupture of the balloon during
dilation. Pliability refers to formability into different shapes,
rather than elasticity. In particular, when delivered by the
catheter, the dilatation balloon is evacuated, flattened and
generally wrapped circumferentially about the catheter in its
distal region. Thin, pliable dilatation balloon walls facilitate a
tighter wrap that minimizes the combined diameter of the catheter
and the balloon during delivery. Furthermore, pliable balloon walls
enhance the catheter "trackability" in the distal region, i.e., the
ability of the catheter to bend in conforming to the curvature in
vascular passages through which it must be routed in reaching a
particular treatment site.
One method of forming strong, pliable dilatation balloons of
polyethylene terrathalate (PET) is disclosed in U.S. Pat. No. RE.
33,561 (Levy). A tubular parison of PET is heated at least to its
second order transition temperature, then drawn to at least triple
its original length to axially orient the tubing. The axially
expanded tubing is then radially expanded within a heated mold to a
diameter about triple the original diameter of the tubing. The form
of the mold defines the aforementioned medial section, shafts and
cones, and the resulting balloon has a burst pressure greater than
200 psi.
Such balloons generally have a gradient in wall thickness along the
cones. In particular, larger dilatation balloons, e.g., 3.0-4.0 mm
diameter (expanded) tend to have a wall thickness in the working
length in the range of from 0.010 to 0.020 mm. Near the transition
of the cones with the working length or medial section, the cones
have approximately the same wall thickness. However, the wall
thickness diverges in the direction away from the working length,
until the wall thickness near the proximal and distal shafts is in
the range of 0.025 to 0.040 mm near the associated shaft or
stem.
The increased wall thickness near the stems does not contribute to
balloon hoop strength, which is determined by the wall thickness
along the balloon medial region. Thicker walls near the stems are
found to reduce maneuverability of the balloon and catheter through
a tortious path. Moreover, the dilatation balloon cannot be as
tightly wrapped about the catheter shaft, meaning its delivery
profile is larger and limiting the capacity of the catheter and
balloon for treating occlusions in smaller blood vessels.
U.S. Pat. No. 4,963,133 (Noddin) discloses an alternative approach
to forming a PET dilation balloon, in which a length of PET tubing
comprising the parison is heated locally at opposite ends and
subjected to axial drawing to form two "necked-down" portions,
which eventually become the opposite ends of the completed balloon.
The necked-down tubing is then simultaneously axially drawn and
radially expanded with a gas. The degree to which the tubing ends
had been necked-down is said to provide control over the ultimate
wall thickness along the walls defining the cones. However, it is
believed that the use of the Noddin method results in balloons
exhibiting a comparatively low burst pressure.
Copending application Ser. No. 08/582,371, filed Jan. 11, 1996,
U.S. Pat. No. 5,733,301 describes a method for reducing cone
stiffness by using a laser to ablate and remove polymeric material
from the cone areas after the balloon is blown. It is preferable
that the desired result be obtained during the balloon molding
operations obviating the need for additional post molding
operations.
Therefore, it is an object of the present invention to provide a
method for stretch blow molding dilatation balloon having a high
burst pressure and hoop strength, but with reduced material mass in
the balloon cones, thus reducing cone stiffness and improving the
trackability, crossing profile, stenosis recross and balloon
retrieval, via a guiding catheter.
SUMMARY OF THE INVENTION
To achieve these and other objects of the invention, there is
provided a method of making dilatation balloons with reduced cone
stiffness. The method comprises the steps of first providing a mold
having a cavity including a cylindrical center segment defining a
working length of a dilatation balloon body where the center
segment is of a predetermined diameter. The mold cavity also
includes two opposed end segments, each having an arcuate cone
shape tapering from the predetermined diameter of the center
segment to a smaller desired balloon shaft diameter. The side edges
of the mold are dimensioned to be within about 0.05 in. of the
termination point of the arcuate cone at the smaller desired
balloon shaft diameter.
Next, a tubular polymeric parison of a predetermined diameter and
wall thickness is placed with a mold and the parison has the
opposed ends thereof extending beyond the side edges of the mold,
the opposed ends being clamped in a tensioning fixture. The mold is
heated to bring the temperature of the parison near or above the
glass transition temperature of the polymeric material comprising
the parison. The tensioning fixture is then longitudinally
displaced relative to the mold to initially longitudinally stretch
the parison by a predetermined amount to introduce a degree of
longitudinal orientation and to neck down the tubular parison to a
lesser diameter.
Following this initial longitudinal stretch, a second longitudinal
stretching operation is initiated and as the tensioning fixture is
being moved to achieve a second stretch, a gas is injected into the
tubular parison to radially expand the parison to a limit defined
by the mold cavity. At this point, the wall thickness in the
working length of the balloon and in its cones is a function of the
degree of longitudinal and radial stretching as well as the gas
pressure applied to effect the radial expansion.
Following inflation of the balloon within the mold, a third
longitudinal stretch is performed by further displacing the
tensioning fixtures relative to the mold. It is the third stretch
within the above-described mold that is found to remove material
from the cone area as the tubing is drawn down to a desired size
for a catheter shaft. Removal of material from the cone area
renders them more pliable than balloons prepared in the same way
but not subjected to longitudinal stretching following the radial
expansion of the balloon within the mold. The third stretch also
creates an increased number of nucleation sites for crystallization
to occur.
After the third stretch operation is terminated, the temperature of
the mold is increased such that the biaxially oriented balloon
reaches its crystallizing temperature for effectively locking the
molecular structure in place.
Following crystallization, the mold is cooled below the glass
transition temperature of the polymer so that the crystallization
structure of the balloon is not lost. Once the mold has
sufficiently cooled, it can be opened and the balloon removed.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top elevational schematic view of the equipment used in
carrying out the method of the present invention;
FIG. 2 is an enlarged view of one of the jaws of the mold showing
the desired profile of the mold cavity used in preparing dilatation
balloons having reduced cone stiffness;
FIG. 3 is a drawing helpful in understanding the manner in which
the mold cavity shape is arrived at; and
FIG. 4 is a flow chart of the steps employed in preparing
dilatation balloons exhibiting reduced cone stiffness.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, there is illustrated schematically the
apparatus for stretch blow molding dilatation balloons for later
assembly on to catheter body stock in the fabrication of dilatation
balloon catheters. The mold itself is indicated generally by
numeral 10 and comprises first and second mold halves 12 and 14
which when abutting one another at a parting line 16 define an
internal mold cavity 18. The mold halves or jaws can be opened or
spread apart to allow placement of a tubular parison therein. The
opposed ends of the parison 22 and 24 are clamped in a tensioning
fixture including clamping jaws 26 which are mounted on rails 28
and 30 for longitudinal movement therealong.
As those skilled in the art appreciate, the mold 10 incorporates
heating elements (not shown) and appropriately positioned
temperature sensors for monitoring the mold temperature and sending
temperature information back to a microprocessor-based controller
for maintaining precise closed-loop control of the temperature of
the mold and of the parison contained in it. Likewise, a suitable
linear encoder (not shown) is operatively coupled to the
translatable clamping fixtures 26 to provide positional information
to the microprocessor-based controller whereby the degree of
longitudinal stretch imparted to the parison 20 can be precisely
controlled.
The equipment for stretch blow molding shown in FIG. 1 also
includes a means for introducing a gas 32, under pressure, into the
lumen of the tubular parison 20 and for monitoring and controlling
that pressure again, using closed-loop control.
Except for the mold cavity 18 formed in the mold halves 12 and 14,
the equipment used in carrying out the method of the present
invention is altogether conventional. The mold cavity employed is
unique, as is the operation whereby the cone segments of the
balloons to be formed in it are made to contain less material than
in conventional designs.
FIG. 2 is a view looking at the interior of one of the jaws 12 or
14 and showing the preferred profile of the mold cavity 18.
The portion of the balloon between the dashed construction lines
A-A define the working length of a dilatation balloon formed
therein and this portion of the balloon is generally cylindrical.
The portion of the mold between construction lines A and B form the
cones and, as can be seen from FIG. 2, the cones do not have a
linear taper. They are slightly arcuate in the zone between the
construction lines A and B. The portion of the mold between the
construction lines B and C will ultimately comprise the shaft
portion of the balloon formed in the mold cavity 18.
The following table sets out typical mold dimensions in stretch
blow-molding a dilatation balloon having a working length of 20 mm
and an expanded diameter of 4.0 mm. These dimensions are
illustrative only because the various dimensions change depending
upon the size of the balloon to be formed.
TABLE I Dimension Magnitude (Inches) A-A .763 B-B 1.532 C-C 1.557
B-C .025 A-B .372 R.sub.1 .882 R.sub.2 1.010
With reference to FIG. 3, for any size balloon diameter, the
radiused balloon ends of the mold are designed using the following
graphical construction technique:
1. The horizontal centerline 32 for the mold is first
established.
2. Construction lines 34 above and below the horizontal center line
32 are established to define the desired balloon diameter.
3. Construction lines 36 above and below the center line establish
the desired balloon shaft diameters for both the proximal and
distal ends.
4. The vertical center line 38 for the mold is set.
5. Lines 40 and 40' define the desired working length of the
balloon body on either side of the vertical center line 38.
6. Construction lines 42 are created at the points of intersections
of lines 36 and 40 such that lines 42 form a desired angle with
respect to line 36. An angle of 12.degree. is typical. Each of
lines 42 should cross the horizontal center line 32 of the mold.
Construction lines 42 determine the length of the end of the
balloon.
7. Construction line 44 is created at the intersection of lines 36
and 42. Construction line 44 indicates the boundary for the end of
the balloon and the transition to the balloon shaft.
8. Arcs 46 are next constructed. Arc 46 is a three point arc, and
it should pass through the intersection of lines 34 and 40, and
lines 42 and 44. The end point of the arcs 46 should be chosen so
that they are tangent to line 34 at the intersection of lines 34
and 40.
9. Construction lines 42 can now be erased and the portion of the
arcs 46 to the left (outside) of construction line 44 can also be
erased.
10. Displace construction line 44 to the left by 0.025 in. to 0.25
in. establish the left end of the mold which is depicted in FIG. 3
by construction line 48.
11. The lines 36 to the right (inside) of construction line 44 and
to the left (outside) of construction line 48 are trimmed to form
the short land of the mold.
12. Construction line 44 can now be erased and lines 34 trimmed to
the left (outside) of line 40 of the left half of the mold.
13. The foregoing construction steps are then repeated for the
right side of the mold to form the other balloon end.
As will be explained in further detail hereinbelow, by providing
the arcuate cone segments and the short cylindrical shaft segments
(dimension B-C in Table I), it is possible to remove polymeric
material from the cone portions of the mold by providing a third
stretch to the parison following inflation of the parison to
achieve radial orientation.
Using the mold created using the techniques outlined above in the
apparatus of FIG. 1, dilatation balloons exhibiting a reduced cone
thickness as compared to prior art stretch blow molding operations
can be achieved. Referring to FIG. 4, there is illustrated a flow
chart of the steps used to prepare such improved dilatation
balloons. In carrying out the method, a precut length of a suitable
tubular parison is placed in the mold so as to span the mold cavity
in the longitudinal direction. The opposed ends of the parison are
clamped by the tensioning member 26. The mold is partially closed
about the tubular parison 20 and a gas at a relatively low pressure
is introduced into the lumen of the parison and a slight tension is
applied to eliminate sagging of the parison when subsequently
heated.
Following this initial setup and pretensioning, the mold 10 is
heated up to a desired temperature which depends upon the
thermoplastic material involved. Generally speaking, the mold is
heated to a temperature which is above the glass transition
temperature. For PET, the mold may typically be heated to
175.degree.. Once this temperature is reached, the molding
operation can be begin.
The parison is subjected to a first stretching operation to
initiate longitudinal orientation in the plastic. The degree of
stretch varies with the tube size (wall thickness) and the tube
material. This first stretch which for a PET parison may be in the
range of 1/4 in. to 1 1/2 in. at each end thereof, not only results
in some longitudinal orientation, but it also necks down the
original tubing comprising the parison to a smaller diameter.
After the prestretch (first stretch), the mold is completely closed
and a second longitudinal stretch is initiated. During the time
that the second stretch is occurring, the balloon is fully inflated
by injecting an inert, dry gas, e.g., nitrogen, under relatively
high pressure into the lumen of the parison to thereby radially
expand the parison to fill the mold. The gas pressure depends on
tubing thickness and the desired wall thickness of the resulting
balloon but will typically be in the range of from 50 psi to about
400 psi. The wall thickness of the resulting balloon is a function
of both the longitudinal stretch and the radial stretch employed.
There is also an interaction between the pressure and the degree of
longitudinal stretch on the thickness of the resulting balloon
wall. Generally speaking, the higher the pressure, the less the
wall is thinned by the longitudinal stretching.
With continued reference to the flow chart of FIG. 4, following
inflation of the balloon and while the balloon is still subjected
to the pressure of the inflation gas, the parison is longitudinally
stretched a third time. Because of the arcuate shape of the mold in
the zone thereof defining the end cones and because of the short
dimension B-C (FIG. 2 and Table I), the third longitudinal stretch
is effective to remove material from the cone area of the balloon
and to simultaneously draw the tubing down to a desired size
thereby providing a thinner shaft portion for later attachment to
the catheter body.
Defining the stretch ratio as the ratio of the length after the
stretch divided by the length prior to the stretch, for a PET
polymer the first stretch ratio may be in the range of from 1.005
to 2.0, that for the second stretch in the range of from 1.05 to
3.0 and for the third stretch in the range of from 1.1 to 4.0.
Following the third stretch operation, the temperature of the mold
is increased to the crystallizing temperature of the polymer
employed to effectively "freeze" the molecular structure resulting
from the longitudinal and radial orientation in place. The
crystallizing step takes place with the balloon pressurized to the
same inflation pressure earlier applied during the balloon
inflation step. This helps to ensure that the balloon walls in the
working area will remain at the same thickness after the third
longitudinal stretch and subsequent crystallizing.
The mold can now be cooled down back below the glass transition
temperature for the polymer and, following that, the mold can be
opened and the clamps released. The portion of the parison outside
of the mold is then trimmed off and the balloon is ready to be
mounted on a catheter body.
Comparative tests were run on balloons prepared in accordance with
the method of FIG. 4 when using a mold having a profile like that
of FIG. 2 with balloons fabricated using a prior art "two stretch"
molding process having all of the steps of FIG. 4 except the third
stretch following balloon inflation and in a mold that had linear
(rather than arcuate) cone profiles. These specific parameters that
were compared were derived by advancing a plurality of dilatation
catheters having balloons manufactured in accordance with the
method of the present invention and balloons manufactured in
accordance with the described prior art through a test fixture. The
test fixture had a tortuous path and located at differing spots
within the tortuous path were a Palmez-Schatz stent and a
Wallstent.RTM. Endoprosthesis. The purpose of this test was to
evaluate the forces required to push the catheter through the
fixture and the ability of the catheter to pass through each of the
stents without getting caught by the stent's structure. The average
force that was required to pass the conventional catheter through
the test fixture was 695.9 grams. This is to be compared with 390.5
grams required to be applied to the catheters having balloons made
in accordance with the present invention to traverse the same test
fixture. This represents approximately a 44 percent reduction in
tracking force.
A further test was conducted to assess the force required to
re-cross a stenosis following balloon inflation. Balloons made in
accordance with the method of the present invention in the mold
cavity made as described herein showed an approximate decrease of
18 percent in the stenosis recross force when compared to balloons
molded in the conventional "two stretch" process.
Testing further revealed that the balloons molded with the "three
stretch" process of the present invention required the lowest force
to withdraw the balloon catheter through a guiding catheter. The
force to withdraw the balloons prepared in the three stretch
process was about 28% less than the force necessary to withdraw
balloons made using the prior art two stretch process.
Balloons made in accordance with the three stretch process of the
present invention were able to be guided through the stent blocks.
The conventional balloons made using the two stretch process were
not capable of being pushed through the stents, even with
considerable effort.
The improved performance of dilatation balloons made in accordance
with the present invention is believed to be due to the extraction
of material from the cone areas of the balloon taking place during
the third stretch. The process of the present invention produces a
high degree of molecular orientation, yielding balloons with high
strength and simultaneously a reduced balloon wall thickness,
balloon cone thickness and balloon shaft diameter. This eliminates
the need for subsequent balloon processing following the balloon
blowing operation.
* * * * *